1. Field of the Invention
The present invention relates to a caulking pin for use in connecting light shielding blades to actuation arms for use in shutters and apertures of cameras, and more particularly to a caulking pin for use in high speed camera shutter and aperture mechanisms.
2. Description of the Related Art
In recent years, due in part to improvements in film speed, cameras have come on the market having, shutter speeds as high as 1/8000th of a second and strobe synchronization speeds in the range of 1/2501th of a second. Designing shutter and aperture mechanisms capable of handling such high speeds has proven difficult due to the close proximity each light shielding blade has with the adjacent light shielding blades.
Conventional focal plane shutters typically have a main arm and a subarm, which are respectively connected to a shutter base and multiple divided shielding blades. These connections typically use a caulking pin joint which allow the blades to rotate freely in a parallel linkage. When the shutter is open, the separate light-shielding blades are folded on top of each other at the outside of the exposure window. In order to close the shutter, the drive arm causes the blades to slide past each other and unfold, thereby covering the exposure window. Generally, the blades are rotated from the spread-out position into the folded position and placed on top of another. As the blades must lie extremely close together, in order to block incoming light, the tolerances in the construction of the shutter are very tight.
FIG. 6 shows the structure of a conventional caulking pin joint. An arm 1 is rotatably connected to a light shielding blade 2 via caulking pin 3. Caulking pin 3 comprises a disc-shaped body 3a having a circular protrusion 3c depending there from. The circular protrusion 3c has a smaller diameter than the disc-shaped body 3a and is adapted for insertion into an insertion hole in arm 1. Depending from the circular protrusion 3c, is a hollow circular section 3b having a diameter smaller than the circular protrusion 3c. The diameter of the hollow circular section 3b is such that it is adapted to fit within an insertion hole in light shielding blade 2. Prior to assembly, the light shielding blade 2 undergoes an embossing finishing through press molding, such that the section around the insertion hole is raised, via slanted section 2a, so as to be on a different plane from the remainder of the blade 2b. After insertion into the arm and light shielding blade, the circular hollow portion 3b of caulking pin 3 is spread outwards, i.e., deformed, causing the light shielding blade 2 to be held between the flat surface of the circular protrusion 3c and the deformed circular section 3b (shown by the dotted line).
Looking at FIG. 7, because the perimeter section 2a of the insertion hole light shielding blade 2 slants upward with respects to the rest of the blade 2b, the deformed hollow circular section does not protrude past the planar section of the light shielding blade 2b. This allows another light shielding blade 4 to be placed on top of light shielding blade 2 and provides clearances such that neither blade will collide with the other.
The main problem with the existing caulking pin pivot joint, as shown in FIGS. 6 and 7, is a deterioration in strength of both the light shielding blade and the caulking pin joint due to the extreme embossing performed on the light shielding blade 2. Specifically, the embossed section is susceptible to warping and cracking, which not only significantly reduces the strength of the joint, but also causes problems when the affected blade is stacked with other blades. The obvious solution would be to forego the embossing and use a simple flat blade structure. However, when a flat blade is connected to the arm 1 by means of the existing caulking pin 3, as shown in FIG. 6, the blades have a tendency to interfere with other blades due to the protuberance of the circular hollow section 3c. Further, the blades have a tendency to bow, which allows intermittent light past the shutter or aperture. To date, the only solution to this problem has been to increase the spacing between the light shielding blades, allowing some measure of light leakage.
The inventors have discovered the above-noted problems with current caulking pin joints and have developed solutions to these problems.